5.7 Ticking on Acelleration

[1999 Tahoe 4x4]

I have a 1999 5.7 Tahoe. Upon acceleration it makes a ticking noise that sounds exactly like a valve lifter.

 

It is most noticeable with a mild-warm engine AND under light acceleration above 1000rpm. Coasting there is no ticking sound, but at the slightest acceleration the ticking is there. It is not loud but loud enough to hear it with the windows closed and driving with or without lowfan-A/C.

The ticking has the frequency about one tick for every explosion in e.g cylinder Nr.1 (just an example, don't know if it is coming from Nr.1 cylinder). However this ticking is more related to a combination of engine load and rpm. It is absolutely not related to any kind of vehicle movement. At idle it is hardly noticeable and revving up the engine in neutral without load does not produce this ticking sound. It is very difficult to pinpoint where it is coming form.

So far I could only find that it is SURE coming from the driver side as during idle it is noticeable in the driver side wheel well and absolutely not noticeable in the passenger side wheel well. Open hood impression supports driver side as well.

It is definitely not coming from any accessory belt driven devices. Using a Mechanics Stethoscope, I can't hear anything on the exhaust manifold, can't hear anything touching/listening at the rocker cover, and can't hear anything at any openly accessible part of the fuel injection system. The only time I hear something is if I open the oil fill cap and listen through the cap. There is a light tapping noise that resembles this ticking.

Back in the car and ready to drive; if I put it in gear and step on the brakes and try to rev the engine about at 1200-1300 rpm, which is about where the torque converter holds the engine back, the sound does appear sometimes slightly. But it seems like this kind of test is too much load for the sound to appear clearly.

 

Trying to cure it, I did an engine flush with AMSOIL, tied to use different viscosity oils, I have changed EGR, Thermostat, PCV, Plugs+Wires+Distributor I have even installed the three baffles in the Secondary Injection Hose as some of the Technical Bulletin suggested. Further I have tried to change/vary the location of these baffles and I also have changed both check valves of the Secondary Air Injection System. No changes, the sound is still there. Besides that everything runs just fine. The Snap-On scanner shows I have no DTC codes. I have this problem since over one year and 10.000 miles. No changes, does not get worse or better. This noise drives me nuts. Does anyone have any ideas what this is?

 

Can a leak at the exhaust manifold sound like this and have this symptoms?

[95Sierra2500]

Yes, an exhaust leak at the manifold can and will sound like this. I've got one on my '95 right now. It's probably an exhaust donut, as those go bad before manifold gaskets do.

[1999 Tahoe 4x4]

Thanks.

 

So are you saying that sometimes like in my case there is a chance that SOME KIND of exhaust leak can be actually heard better with mild warm engine than with cold engine? Donought is the part where the Exhaust Manifold meets the Y-Pipe of the Catalytic Converter right? Let me know and I will take that thing apart right away.

[Wingnut]

Also sounds like maybe a bad knock sensor.

[SimplyRAD]

Thanks.

 

So are you saying that sometimes like in my case there is a chance that SOME KIND of exhaust leak can be actually heard better with mild warm engine than with cold engine?  Donought is the part where the Exhaust Manifold meets the Y-Pipe of the Catalytic Converter right? Let me know and I will take that thing apart right away.

 

<{POST_SNAPBACK}>

 

 

 

Just the opposite... heat expands the metal... so in theory, if it is a small leak, it should quiet down or seal up when the pipes get hotter.

 

I just fixed my leak and yes it produced a ticking sound. Only when pipes were cold though. My leak occurred at the end of my headers where it connects to the pipes just before the cat. I have a true dual exhaust so all I did was tighten them all including the connection to the heads. The bolts surprisingly became loose.

 

Before dismantling your exhaust, check for carbon build up along the pipes. You will see if you indeed have a leak in the exhaust. If so, you found the culprit. If its in the pipes, weld up the hole or replace if it severly damaged. You should be able to fix the leak without taking the exhaust off if the leak is attainable.

[95Sierra2500]

Thanks.

 

So are you saying that sometimes like in my case there is a chance that SOME KIND of exhaust leak can be actually heard better with mild warm engine than with cold engine?  Donought is the part where the Exhaust Manifold meets the Y-Pipe of the Catalytic Converter right? Let me know and I will take that thing apart right away.

 

<{POST_SNAPBACK}>

 

 

 

Yeah I think I misread your original post, I thought you said it got quieter when it heated up. However, it does still sound like an exhaust leak, perhaps in a bend in your y-pipe on the outside where expansion would make the hole larger? I'd definately say inspect your exhaust system throughly, sounds like you've got a leak somewhere.